rust: Add soc_device support

Allow SoC drivers in Rust to present metadata about their devices to
userspace through /sys/devices/socX and other drivers to identify their
properties through `soc_device_match`.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Link: https://patch.msgid.link/20251226-soc-bindings-v4-1-2c2fac08f820@google.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

2 files changed, 137 insertions, 0 deletions

diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index f812cf120042..6d637e2fed1b 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -138,6 +138,8 @@ pub mod security;
 pub mod seq_file;
 pub mod sizes;
 pub mod slice;
+#[cfg(CONFIG_SOC_BUS)]
+pub mod soc;
 mod static_assert;
 #[doc(hidden)]
 pub mod std_vendor;
diff --git a/rust/kernel/soc.rs b/rust/kernel/soc.rs
new file mode 100644
index 000000000000..0d6a36c83cb6
--- /dev/null
+++ b/rust/kernel/soc.rs
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (C) 2025 Google LLC.
+
+//! SoC Driver Abstraction.
+//!
+//! C header: [`include/linux/sys_soc.h`](srctree/include/linux/sys_soc.h)
+
+use crate::{
+    bindings,
+    error,
+    prelude::*,
+    str::CString,
+    types::Opaque, //
+};
+use core::ptr::NonNull;
+
+/// Attributes for a SoC device.
+///
+/// These are both exported to userspace under /sys/devices/socX and provided to other drivers to
+/// match against via `soc_device_match` (not yet available in Rust) to enable quirks or
+/// device-specific support where necessary.
+///
+/// All fields are freeform - they have no specific formatting, just defined meanings.
+/// For example, the [`machine`](`Attributes::machine`) field could be "DB8500" or
+/// "Qualcomm Technologies, Inc. SM8560 HDK", but regardless it should identify a board or product.
+pub struct Attributes {
+    /// Should generally be a board ID or product ID. Examples
+    /// include DB8500 (ST-Ericsson) or "Qualcomm Technologies, inc. SM8560 HDK".
+    ///
+    /// If this field is not populated, the SoC infrastructure will try to populate it from
+    /// `/model` in the device tree.
+    pub machine: Option<CString>,
+    /// The broader class this SoC belongs to. Examples include ux500
+    /// (for DB8500) or Snapdragon (for SM8650).
+    ///
+    /// On chips with ARM firmware supporting SMCCC v1.2+, this may be a JEDEC JEP106 manufacturer
+    /// identification.
+    pub family: Option<CString>,
+    /// The manufacturing revision of the part. Frequently this is MAJOR.MINOR, but not always.
+    pub revision: Option<CString>,
+    /// Serial Number - uniquely identifies a specific SoC. If present, should be unique (buying a
+    /// replacement part should change it if present). This field cannot be matched on and is
+    /// solely present to export through /sys.
+    pub serial_number: Option<CString>,
+    /// SoC ID - identifies a specific SoC kind in question, sometimes more specifically than
+    /// `machine` if the same SoC is used in multiple products. Some devices use this to specify a
+    /// SoC name, e.g. "I.MX??", and others just print an ID number (e.g. Tegra and Qualcomm).
+    ///
+    /// On chips with ARM firmware supporting SMCCC v1.2+, this may be a JEDEC JEP106 manufacturer
+    /// identification (the family value) followed by a colon and then a 4-digit ID value.
+    pub soc_id: Option<CString>,
+}
+
+struct BuiltAttributes {
+    // While `inner` has pointers to `_backing`, it is to the interior of the `CStrings`, not
+    // `backing` itself, so it does not need to be pinned.
+    _backing: Attributes,
+    // `Opaque` makes us `!Unpin`, as the registration holds a pointer to `inner` when used.
+    inner: Opaque<bindings::soc_device_attribute>,
+}
+
+fn cstring_to_c(mcs: &Option<CString>) -> *const kernel::ffi::c_char {
+    mcs.as_ref()
+        .map(|cs| cs.as_char_ptr())
+        .unwrap_or(core::ptr::null())
+}
+
+impl BuiltAttributes {
+    fn as_mut_ptr(&self) -> *mut bindings::soc_device_attribute {
+        self.inner.get()
+    }
+}
+
+impl Attributes {
+    fn build(self) -> BuiltAttributes {
+        BuiltAttributes {
+            inner: Opaque::new(bindings::soc_device_attribute {
+                machine: cstring_to_c(&self.machine),
+                family: cstring_to_c(&self.family),
+                revision: cstring_to_c(&self.revision),
+                serial_number: cstring_to_c(&self.serial_number),
+                soc_id: cstring_to_c(&self.soc_id),
+                data: core::ptr::null(),
+                custom_attr_group: core::ptr::null(),
+            }),
+            _backing: self,
+        }
+    }
+}
+
+#[pin_data(PinnedDrop)]
+/// Registration handle for your soc_dev. If you let it go out of scope, your soc_dev will be
+/// unregistered.
+pub struct Registration {
+    #[pin]
+    attr: BuiltAttributes,
+    soc_dev: NonNull<bindings::soc_device>,
+}
+
+// SAFETY: We provide no operations through `&Registration`.
+unsafe impl Sync for Registration {}
+
+// SAFETY: All pointers are normal allocations, not thread-specific.
+unsafe impl Send for Registration {}
+
+#[pinned_drop]
+impl PinnedDrop for Registration {
+    fn drop(self: Pin<&mut Self>) {
+        // SAFETY: Device always contains a live pointer to a soc_device that can be unregistered
+        unsafe { bindings::soc_device_unregister(self.soc_dev.as_ptr()) }
+    }
+}
+
+impl Registration {
+    /// Register a new SoC device
+    pub fn new(attr: Attributes) -> impl PinInit<Self, Error> {
+        try_pin_init!(Self {
+            attr: attr.build(),
+            soc_dev: {
+                // SAFETY:
+                // * The struct provided through attr is backed by pinned data next to it,
+                //   so as long as attr lives, the strings pointed to by the struct will too.
+                // * `attr` is pinned, so the pinned data won't move.
+                // * If it returns a device, and so others may try to read this data, by
+                //   caller invariant, `attr` won't be released until the device is.
+                let raw_soc = error::from_err_ptr(unsafe {
+                    bindings::soc_device_register(attr.as_mut_ptr())
+                })?;
+
+                NonNull::new(raw_soc).ok_or(EINVAL)?
+            },
+        }? Error)
+    }
+}